JPS5953778B2 - Method and device for detecting short circuits in AC lines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detecting short circuits in AC lines.

In this case, a short circuit in the alternating current line is detected by detecting the time course of the voltage and current at the measuring point in the form of a measured voltage um and a measured current im.

Detection of short circuits in the line is a prerequisite for the subsequent protective measures taken.

Therefore, after a short circuit has been detected, a fault location is carried out or the fault point is localized to a well-defined line section.

In this sense, short circuit detection constitutes an essential part of line or line network protection systems.

Fault point location, fault localization, fault detection and subsequent fault identification are performed in a wide variety of ways.

Therefore, it is important to detect failures using an appropriate circuit device.
It has become an independent technology and a challenge.

Typically, fault or accident detection is carried out, for example using the "Brown-Boveri M
J Vol. 53, No. 11/12, 7
This is done using a minimum impedance method and corresponding relays as described on page 88.

This kind of scheme is based on the comparison of current and voltage.

That is, it responds to an increase in current representing a short circuit at the measurement point and a correspondingly large drop in line voltage.

In the known method, the signals belonging to the measured voltage and the measured current are rectified and a difference between the rectified signals is formed.

In this case, the zero crossing of the difference signal determines the integration period of the subsequent integration with a predetermined rise rate.

Therefore, since the amplitude or magnitude obtained by time integration is a function of the relationship between the measured voltage and the measured current, a predetermined limit value of time integration is correlated to the voltage-current relationship that occurs during a short circuit, and the result of the integration is Based on whether the line is below or above the limit value, it can be determined whether the line is in a normal state or in a faulty state.

Since the failure detection time in known detection methods and devices, including the above-mentioned examples, is relatively long, there is a need to shorten the detection time in order to take protective measures quickly.

Therefore, an object of the present invention is to provide a fault detection method and apparatus that can further reduce the fault detection time.

According to the present invention, this problem is solved as follows.

That is, in a method of the type mentioned at the outset, from the measured voltage and current, or quantities derived therefrom,
Generate traveling wave signals of the following form that travel in mutually opposite directions, a (t)-k・ (um+Rw-1m)a (t)
==k"('m+Rw" im) where um is the measured voltage or a quantity derived from it, im is the measured current or a quantity derived from it, Rw is the impedance coefficient, and k is freely selectable It is a constant of proportionality, and traveling wave signals (a
(t).

b (t)), the phase relationship between at least one frequency component of each frequency component is monitored as a quantity representing the line condition.

Further, the apparatus according to the present invention is configured as follows.

That is, a measuring voltage channel connected to a voltage measuring device and a measuring current channel connected to a current measuring device and containing a constant number multiplier are connected in parallel to an adder circuit and a subtracter circuit, and the output sides of these two circuits are connected in parallel. They connected it to a phase angle detector.

The method according to the invention is based on the formation and evaluation of traveling wave signals traveling in opposite directions.

This traveling wave signal is formed at the measurement point.

Moreover, the time course corresponds to the time course of a traveling wave traveling in the opposite direction on the track (when observed at the measurement point).

The impedance coefficient Rw, which determines the ratio of the measured voltage-dependent signal component to the measured current-dependent signal component, can be adjusted within a relatively wide range.

However, in order to reliably detect the weakest short circuit phenomenon detectable at the measurement point, RW must be maintained at a minimum value i so that an impedance below this impedance coefficient Rw does not occur.

Here, the weakest short-circuit phenomenon that can be detected at a measurement point is a short-circuit with the maximum possible arc impedance or fault impedance that occurs at the point farthest from the measurement point.

2. By approximating the above impedance coefficient to a value corresponding to the characteristic impedance of the line, special traveling wave signals corresponding to traveling waves traveling in opposite directions can be obtained.

In that case, the amplitude of these traveling waves traveling in opposite directions would be reduced only by attenuation, but would otherwise have a certain profile along the line.

It also propagates at a predetermined propagation speed.

For additional fault location operations, such as determining the distance and direction to the fault point, it is advantageous to use the above-mentioned special traveling wave signal or its approximation signal.

However, regarding fault detection handled by the present invention, for example, if transient frequency components other than the dominant line frequency component account for a small proportion of the measured signal, even if the impedance coefficient deviates greatly from the characteristic impedance of the line, That's acceptable.

Furthermore, according to the method of the invention, the formed traveling wave signals traveling in mutually opposite directions are monitored for the phase relationship between their frequency components.

The frequency components in this case are advantageously line frequency components.

The phase relationship between the frequency components of a traveling wave signal changes dramatically when a short circuit occurs in the line.

When a normal AC line for power transmission is operating normally, the dominant line frequency components of traveling wave signals traveling in opposite directions are substantially in phase with each other.

But when a short circuit occurs, it becomes approximately in phase.

This is based on the following reasons.

That is, while the current component of the traveling wave signal is smaller than the voltage component during normal operation, the voltage component becomes smaller than the current component when a failure occurs.

Therefore, the phase relationship between line frequency components of a traveling wave signal, or any other suitable frequency component, is continuously monitored and the phase variation is adjusted by a predetermined minimum amount corresponding to the level of disturbance in question. When exceeded, this can be used as a detection criterion.

Since the above change in phase relationship from anti-phase to in-phase occurs rapidly, if the phase relationship is monitored as proposed by the present invention, amplitude comparison, which is generally possible only once every half cycle, can be used. The detection time can be significantly reduced compared to conventional methods.

Moreover, this detection time is not restricted by the period of the frequency component to be observed.

This advantage also applies if phase monitoring is combined with integral and time integral limit value monitoring.

This is because in this case as well, continuous phase monitoring allows the integration operation to start without delay and provides an integration time that is independent of the period.

Next, the embodiment shown in the drawings will be described in detail.

Referring to Figure 1, a track consisting of an elevated line 1 extending in the direction of arrow X is provided with a measuring section 2 at a measuring point It is assumed that

The measurement unit 2 includes a voltage transformer 2a that generates a measurement voltage um as an output signal, and a current transformer 2b that generates a measurement current im as an output signal.

The measuring voltage and measuring current can then be obtained in the form of voltage signals of corresponding values.

The measured current is multiplied by the impedance coefficient Rw in the constant multiplier 3! do.

The magnitude of this impedance coefficient is determined by at least the maximum line input impedance (maximum arc) that appears at the time of a fault.
impedance + maximum line impedance).

The measuring current is then applied in parallel with the measuring voltage to the first summing amplifier 4 as well as to the first subtracting amplifier 5.

At the output side of these amplifiers, two traveling wave signals traveling in opposite directions appear as shown in the following equation (these two
The two traveling wave signals are further multiplied by a freely selectable conversion factor k).

a (t) -um + Rw-1m b (t) = -um + RW-im (1) In other words, these signals are expressed as follows: have a correlated time course.

In connection with the present invention, it should be noted that this correlation holds true even if the original measurement signal, ie the measurement voltage and the measurement current, are varied in various ways.

For example, even if a corresponding filtering is performed to emphasize one frequency component, especially when the harmonic component is strong, or if a restriction or other modification is applied to the measured signal, the result is that the harmonics proceed in the opposite direction. The above-mentioned correlation holds true as long as there is no substantial disturbance in the phase relationship between the traveling wave signals.

In this example, it is assumed that the traveling wave signal has a dominant frequency component corresponding to one of the line frequencies, not only before the short circuit but also after the short circuit, and therefore no special input filtering is necessary. are doing.

This assumption is approximately commensurate with the actual situation.

The traveling wave signals traveling in opposite directions are modified after passing through a second summing amplifier 4' or a subtracting amplifier 5', which amplifiers are used for the modification function described below. Traveling wave signals a'(t) and b'
(t), for example to a conventional phase detector ph.

At the output of this phase detector, a detection signal d(t) can be obtained which is basically suitable for short-circuit monitoring.

When a traveling wave propagates from the short-circuit point x=z to the measurement point X=0, a sudden change occurs in the phase relationship of the signals a, b or a', b'.

This detection signal d (t) is therefore evaluated only for a very short time.

Furthermore, the traveling wave signals can be used at the outputs A, B for other fault protection purposes, for example for determining the direction and distance of the fault point.

Furthermore, FIG. 1 shows a special phase monitoring circuit, which is likewise connected to the outputs of the circuits 4', 5'.

In this circuit, the traveling wave signal is applied to a function multiplier 6.

The output of this function multiplier 6 generates a corresponding product signal p(t), which product signal p(1) is fed to an integrator 8 with an amplifier 9 and a negative feedback capacitor 10.

The product signal p (t) can itself represent the phase relationship between two traveling wave signals, and therefore can basically be used as a detection signal.

Interfering harmonics are suppressed by the integration performed in the integrator.

A relatively sensitive limit value monitoring is therefore possible with the threshold switch 13 being set to a correspondingly low limit value.

Furthermore, two threshold switches 14 set at high limit values are connected to the output of the integrator 8, which switches have a large response delay at a given rate of rise of the time-integrated signal.

The output of the second threshold switch can be used to check the sensitive fault detection of the first threshold switch with a small delay.

For line frequency components of traveling wave signals traveling in opposite directions, the value of the line input impedance is the impedance coefficient R.
They are substantially out of phase in the region of normal operating conditions and substantially in phase when a short circuit occurs, unless the value of w is less than the value of w.

This is because during normal operation, the current component ° of the traveling wave signal in equation (1) is smaller than the voltage component, whereas during a short circuit, the voltage component is smaller than the current component (
(See Figures 2A and 2B).

In the former case, the product signal p (B) is negative and in the latter case this signal p (t) becomes positive.

During normal operation, the phase difference between line voltage and line current is generally small, so the product signal p (t) becomes negative for a short time.

To obtain a clear signal level under normal operating conditions,
In the circuit of FIG. 1, a diode 12, which essentially operates as a half-wave rectifier, can be connected to the input of the integrator.

This diode completely or partially suppresses the negative value of the product signal or limits it to a small magnitude.

A suppression element connected with such polarity can basically also be connected at the output of the integrator or, as shown in the illustrated example, in parallel with the negative feedback path of the integrator. can.

Discharge resistor 11 resets the integrator to a neutral output state after the fault-induced product signal disappears.

Optionally, a discharge circuit arrangement may be used instead of this discharge resistor, which is activated after fault detection has been carried out in any manner.

Even if the line is operating without failure, if the value of the line input impedance is less than the value of the impedance coefficient Rw, the operating current of the high feeder wire 1 increases, and the current component of the traveling wave signal becomes a voltage component in equation (1). It may become larger.

In such a case, even if no failure occurs, the product signal p(
t) is at a slightly positive level (see Figure 3).

This applies particularly when the impedance coefficient Rw is relatively large, for example set within the range of the characteristic impedance of the line.

Various strategies can be considered, as shown in FIG. 1, to modify the signal ratio for extreme load conditions with the intention of preventing false fault detection in non-fault operating conditions.

For example, for the above purpose, the correction signal 5K is output from a constant multiplier in the form of a potentiometer 3b connected to the measuring voltage channel.
(t) and this signal is additively superimposed on the original traveling wave signal via amplifiers 4' and 5' having input polarities as shown.

Then, a traveling wave signal modified as follows can be obtained.

a'(t)-um(1+K)+Rw-1mb'(t)=
-um(1+K)+Rw-1m(2) In this case, the correction coefficient is set in the potentiometer 3b according to the following equation, for example.

In the above equation, Rw is the impedance coefficient and Rrmn is the given minimum value of the line input impedance in the non-fault condition.

Therefore, the modified product signal can be expressed as:

p (t)−um′ (1+K)2 +Kw”·tm” (4) The quadratic term of um is chosen to be high so as to obtain a sign relationship that is valid over the entire predetermined load range.

In other words, by increasing the quadratic term of um, the signal p (B) is made negative when no fault occurs, no matter what the line input impedance is.

Optionally, the above-mentioned modifications can also be performed in the voltage measurement channel before the addition and subtraction circuits for generating the traveling wave signal.

In this case, for example, a constant multiplier 3, shown by a broken line in FIG.
a is used.

A circuit branch between circuit points C and D is shown in FIG. 1 as a further modification.

This circuit branch is constructed as a correction quantity generating circuit to which the measuring voltage is applied and, in particular, consists of a square amplifier 15 and a constant multiplier in the form of a potentiometer 16 connected downstream thereof.

In this circuit configuration, a correction signal S'K (t)=K'·um'' (5) is generated, and in this case, the correction coefficient ' is given by the following equation.

This modified signal is additively superimposed on the product signal by summing resistors 7 and 17.

Even if the correction coefficient is set in this way, the product signal p(t) can be corrected as desired.

That is, in normal operating conditions, the antiphase relationship of the traveling wave signals can always be maintained.

In other words, the product signal p(t) is modified so that its sign is always negative during normal operation.

This circuit configuration requires a multiplier 15 instead of the simple addition elements 4', 5'.

But it is a traveling wave signal with t a (t), b
(t), so the output A,
Determination of the failure direction and failure distance using B is performed in the same way as in the other examples.

Next, the operating method will be described with reference to FIGS. 2A, 2B, and 3.

As can be seen from FIG. 2A, the measured current im rises significantly above the previous level at the time to.

On the other hand, the measured voltage um changes very little, and only substantially increases in harmonic components.

Such a voltage and current profile corresponds to the actual situation when there is a line short-circuit at a location not very close to the measuring point.

Before and after a short circuit, line frequency components dominate in the measured current and voltage, so no special input filtering is necessary.

FIG. 2B shows the course of traveling wave signals a (t), b (t) traveling in opposite directions before and after a short circuit.

The two signals are at time t. There is a sudden transition from an approximate anti-phase relationship to an in-phase relationship, which also corresponds to the actually measured situation.

Here, time t. is the point in time when the signal indicating the occurrence of a fault reaches the measurement point.

Before a short circuit occurs, the two traveling wave signals may deviate slightly from a precise anti-phase relationship.

Then, as shown in FIG. 3, the time course of the product signal p(t), which should originally be in the negative region, pulsates periodically and enters the positive region, albeit for a short time.

However, this phenomenon can be compensated for by the correction measures described above.

After the occurrence of a short circuit, the product signal p (t) follows a substantially positive course, but may briefly enter the negative region during periodic pulsations.

Parts within this negative region are not useful for detecting faults.

The integral detection signal d (t), also shown in FIG. 3, remains at approximately O due to the suppression circuit described in FIG. 1 during the period in which the product signal before the short circuit is negative.

In this case, there will be a short section where the integral signal is positive, but due to the damping effect of the discharge resistor 15, this section will no longer affect the output of the integrator without any special modification.

Time t.

From then on, the integral detection signal d (t) begins to rise almost uniformly.

As a result, the first threshold switch is triggered when the first limit value S1 is exceeded at time t1, and the second threshold switch is triggered when the second threshold value S2 is exceeded at time t2.

Here, time t.

From each trigger time t1. Although there will be a time delay until t2, it is not a problem.

This delay time is determined solely by the time constant of the integrator, ie by the filtering effect on the high-frequency interference signal.

Also, the product signal is set at time t'1. A direct comparison with two limit values at t'2 can also detect a fault.

In this case, the delay time is reduced and is essentially determined only by the time course of the signal.

The time point 1 to trigger can also be controlled by adjusting the trigger limit value and is thus determined by the level of the jamming signal.

Finally, I would like to make additional comments regarding the purpose, configuration, and advantages of the present invention.

During normal operation, that is, when no fault has occurred on the elevated line 1, the product signal p (t) is mostly negative.

On the other hand, in the event of a failure, the product signal must be positive.

To achieve this, the impedance coefficient Rw
needs to be made as small as possible.

This is because the product signal p (t) is calculated based on the following equation (4).

I) (t) =-um” (1+K) 2+Rw”-
im'' As is clear from Figure 2A, during normal operation,
Since the measured current im is smaller than the measured voltage um, the product signal p
(t) is negative.

However, at time t. After a fault occurs at , the current im becomes greater than the voltage um.

Therefore, the phase relationship between traveling wave signals a (t) and b (t) is as follows at time t.

There is a sudden change from anti-phase to in-phase.

Therefore, by monitoring this phase relationship, failures can be detected very quickly.

In other words, the problem of the present invention, which is to shorten the failure detection time, is solved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the accident or failure detection circuit according to the present invention, FIG. 2A is a time waveform diagram showing the course of the measured voltage um and the measured current im around the point of occurrence of a short circuit, and FIG. 2B is a block diagram of the accident or failure detection circuit according to the present invention. is the associated traveling wave signal a
(t) and b(t), and FIG. 3 shows the product signal p(t) formed from these two traveling wave signals and the product signal obtained from the product signal by half-wave rectification and integration. FIG. 3 is a time-signal waveform diagram showing the detection signal d (t). 2a...Voltage transformer, 2b...Current transformer, 3...
・Constant multiplier, 4, 4'... Addition circuit, 5, 5'...
・Subtraction circuit, ph...phase angle detector, 3a, 3b...
・Correction constant multiplier, 7, 17... Addition circuit, 6...
Function multiplier, 8... Integrator, 12... Half wave rectifier,
13.14... Threshold switch, 16... Potentiometer, 15... Quadratic function generator.

Claims (1)

[Claims] 1. A method for detecting a short circuit in an alternating current line by detecting the time course of the voltage and current at a measuring point in the form of a measured voltage (u,) and a measured current (im). From the measured currents or quantities derived from them, traveling wave signals of the following form traveling in mutually opposite directions are generated, a (t)2k (um+Rw-1m)b (t)
−k ・ (um+Rw” tm) where um is the measured voltage or a quantity derived from it, i is the measured current or a quantity derived from it, RW is the impedance coefficient, and k is a freely selectable It is a constant of proportionality, and traveling wave signals (a
(t). A method for detecting a short circuit in an AC line, characterized in that the phase relationship between at least one frequency component of (t)) is monitored as a quantity representing the line condition. 2 Two traveling wave signals (a
(t) and b (t) are mutually multiplied, and the product signal thus obtained is used as a monitoring quantity representing the phase relationship between at least one frequency component of each traveling wave signal traveling in opposite directions. A method for detecting a short circuit in an AC line according to claim 1, which is used as a method for detecting a short circuit in an AC line according to claim 1. 3 forming a signal whose value and sign correspond to the polarity and magnitude of each of at least one frequency component having an opposite phase relationship of a traveling wave signal traveling in opposite directions; and monitoring whether the integrated signal exceeds a limit value.
Method for detecting a short circuit in an AC line as described in Section 1. 4 in the form of measured voltage (um) and measured current (im),
In a device for detecting short circuits in an alternating current line by detecting the time course of voltage and current at a measuring point, a measuring voltage channel connected to the voltage measuring device 2a and a constant number multiplier connected to the current measuring device 2b are provided. 3 are connected in parallel to an addition circuit 4 and a subtraction circuit 5, and the outputs of both circuits 4, 5 are connected to a phase angle detector ph. Short circuit detection device. 5. The apparatus for detecting a short circuit in an AC line according to claim 4, wherein the output sides of the addition circuit 4 and the subtraction circuit 5 are connected to the input side of the function multiplier 6. 6. A short circuit in an AC line according to claim 4 or 5, in which the output side of the function multiplier 6 is connected to an integrator 8 having at least one threshold value switch 13, 14 connected downstream. detection device.